Best way to go about changing your code for platforms?

I never understood how I would change my code for other platforms like

I know how to change them but I just never like

It is so complicated cause someone with an xbox can have a keyboard

someone with a phone can have a keyboard

I just don't get it

someone reccomended that I use

:LastInputChanged event or something

but I never found out where to go from there because of all the complicated things a device can have

Your concerns are valid. Accommodating for multiple platforms is complicated!

I think the most important thing to keep in mind is that you can't really "develop for PC" or "develop for mobile", etc. You can only "develop for mouse + keyborad", or "develop for touch screen". You're on the right track with using LastInputTypeChanged. See that Wiki article for an example of how to change the UI when the user's input has changed.